The blue-shifting intramolecular C–H···π hydrogen bonds (H-bonds) in conformer I of 1,3-hexadien-5-yne (13HD5Y) and its halogen-substituted derivatives are explored by theoretical calculations. The geometric analysis indicates that the C-H bond in conformer I is shortened in comparison with the non-interacting C-H bond, accompanied by the blue-shifts of the C-H stretching frequency. The formation of H-bonds is verified by the atoms-in-molecules and noncovalent interaction analysis. The H-bond energies are estimated to be -0.5∼-2.2 kcal·mol^-1 by isodesmic reaction method at MP2/aug-cc-pVTZ level, which agree with the trends predicted by the geometrical and topological parameters. The results of the natural bond orbital analysis indicate that the origin of the blue-shifting H-bond may be due to the weak π(C≡C) → σ*(C–H) hyperconjugation interaction and the concomitant increasing in the s-character and polarization of C–H bond. This research provides a rare theoretical evidence to identify an intramolecular blue-shifting CH···π H-bond system.

通过理论计算探索了1,3-己二烯-5-炔（13HD5Y）的构象异构体I中的蓝移分子内C–H··π氢键（H键）及其卤素取代的衍生物。几何分析表明，与非相互作用的CH键相比，构象异构体I中的CH键缩短了，伴随着CH拉伸频率的蓝移。通过分子中原子和非共价相互作用分析验证了H键的形成。在MP2 / aug-cc-pVTZ能级下，通过等渗反应法估计氢键能为-0.5〜-2.2 kcal·mol ^-1，与几何和拓扑参数预测的趋势一致。自然键轨道分析的结果表明，蓝移H键的起源可能是由于弱π（C≡C）→ σ *（C–H）超共轭相互作用，并且伴随s键和C–H键极化的增加。这项研究为鉴定分子内蓝移CH···πH键系统提供了罕见的理论依据。